Plural stage desalting/dehydrating apparatus

ABSTRACT

A desalter/dehydrater having a plurality of electrified coalescing stages in a single vessel wherein the stages are isolated hydraulically to allow parallel or serial stage operation and the emulsion being treated is introduced at one side of the vessel and caused to flow to the opposite side between horizontal planar permeable electrodes. In one embodiment, several electrical stages are operated in parallel to increase vessel throughput capacity. In another embodiment, series operation is employed, wherein each successive stage receives the product from the preceding stage as feed, with fresh water being added. The number of stages is one less than the number of the electrodes.

FIELD OF THE INVENTION

This invention relates to apparatus and process useful for desaltingand/or dehydrating oil-continuous emulsions such as crude petroleumoils, although they can be used in the resolution of other emulsions,which term is herein used as including dispersions. More particularly,the invention relates to improved apparatus and processes of this typeemploying multiple electrode/distributor systems located in a singlevessel.

BACKGROUND OF THE INVENTION

It is conventional to desalt or dehydrate oil-continuous emulsions byintroducing such emulsions directly into an electric treating field ofsufficient intensity to coalesce the suspended droplets of the dispersedphase into massses of sufficient size to gravitate from the oil. Thedispersed phase of such emulsions is composed of a material, usuallyaqueous, that is sufficiently immiscible with the oil to produce aninternal or dispersed phase. Initially, the dispersed droplets are ofsuch small size or are so stabilized that they will not readilygravitate from the oil phase. However, the electric field coalesces suchdispersed droplets, and it is found that the resulting coalesced massesgravitate rapidly from the oil, usually in the same container as that inwhich electric treatment takes place. In a desalting operation, aquantity of water may be mixed with the incoming crude oil in a valve orother mixer, all as well known, so that a more complete removal of saltfrom the oil may be accomplished. Typical of such prior artdehydrator/desalters are those described in the folowing U.S. Pat. Nos.:1,838,922, 2,527,690, 2,880,158, 3,206,686, 3,577,336, 2,033,446,2,543,996, 2,892,768, 3,250,695, 3,649,516, 2,041,954, 2,557,847,2,894,895, 3,458,429, 3,672,127, 2,072,888, 2,848,412, 2,963,414,3,592,756, 3,736,245, 2,443,646, 2,855,360, 3,141,000, 3,531,393, andGerman Pat. No. 1,014,076 (Helmut Stock; Aug. 22, 1957).

U.S. Pat. Nos. 4,149,958 and 4,182,672 to Robert B. Martin discloseapparatus and processes for desalting or dehydrating emulsions of thetype above described, wherein the apparatus has a plurality ofelectrified coalescing stages in a single vessel, wherein the stages arehydraulically susbstantially independent and adapted for parallel orseries stage operations. The expression "electrified" denotes thepresence of an electric field, as above described. In one embodimentshown by Martin, two or more electrified stages, each separatelyenergized, are operated in parallel to proportionately increase vesselthroughput capacity. In another embodiment, especially designed fordesalting, series operation is employed, wherein each successive stagereceives the product of the preceding stage as feed, with fresh and/orrecycled water being added.

The embodiments specifically illustrated and described in the Martinpatents incorporate centrally positioned emulsion inlet distributorsbetween horizontally disposed planar permeable electrodes in verticallyspaced relationship. These distributors decrease the effective spacebetween electrodes unless the top and bottom electrodes are providedwith humps to allow more clearance between the distributors and theelectrodes. Alternatively, if the electrodes are not provided withhumps, the top electrode would, in practice, have a hole in it whichwould be directly above the distributor so that the distributor, whichis at ground potential, would be electrically separated from the topelectrode by at least the same distance as between adjacent electrodes.A similar hole and clearance would be needed for the other electrodes.

The necessity for humps in the bottom and top electrodes and/or centralholes in the electrodes creates clearance and design problems. Moreover,if the center electrode in the two stage treaters of Martin U.S. Pat.Nos. 4,149,958 and 4,182,672, with a double box distributor arrangement,is energized rather than grounded, it would require such electrode to bein two separate parts, one on each side of the distributor assembly.

Further, in Martin's specific embodiments of the series plural stagedesalter, collectors at each side of the treating vessel are provided inall but the final stages. These have to be tied together hydraulicallyand balanced to draw equally from each side.

It is an object of this invention to provide a plural stagedehydrating/desalting apparatus, especially useful for desalting crudeoil which avoids the above discussed problems of the Martin apparatusreferred to.

It is a further object of this invention to provide such adehydrating/desalting apparatus which accomodates a separate distributorfor each stage with a minimum of lost electrode area and which isadapted to the use of a middle energized electrode as a single unit,which is easier to hang on insulators and charge.

It is still a further object of this invention to provide improvedprocesses for dehydrating or desalting crude oil employing improvedplural stage dehydrating/desalting apparatus.

Additional objects of the invention will be evident to those skilled inthe art in the course of the following description.

SUMMARY OF THE INVENTION

The above and other objects of the invention are achieved by providingan apparatus for desalting or dehydrating oil-continuous oil-wateremulsions, which has a plurality of electrified hydraulicallyindependent coalescing stages in a single vessel, each stage beingdefined by parallel horizontally disposed planar permeable electrodes invertically spaced relationship, each stage having distributor means forsupplying emulsion associated therewith, the distributor means beingpositioned at one side of the vessel and being adapted to cause emulsionto flow to the opposite side between adjacent electrodes inhydraulically substantially independent flow. The number of stages isone less than the number of electrodes.

As adapted for two stage serial desalting, the apparatus comprises aclosed vessel provided with three horizontally disposed permeable planarelectrodes in vertically spaced relationship, the electrodes and thevessel interior being adapted and arranged to permit water to passdownwardly through the electrodes to the lower portion of the vessel;first stage distributor means and conduit means for supplying oil-wateremulsion thereto; such distributor means being positioned at one side ofthe vessel and adapted to cause the emulsion to flow to the oppositeside of the vessel between the bottom and middle electrode; meanspositioned at such opposite side for collecting the treated first stageproduct; second stage distributor means and conduit means for supplyingemulsion thereto, such distributor means being positioned at the sameside of the vessel as the first stage distributor means and adapted tocause emulsion to flow to the opposite side of the vessel between thetop and middle elctrode; product withdrawal and outlet means in theupper portion of the vessel; and water withdrawal means in the lowerportion of the vessel.

The two stage serial desalting apparatus is further provided with firststage mixing means, conduit means for supplying oil feed and waterthereto, such mixing means being adapted to supply oil-water emulsion tothe first stage distributor means; second stage mixing means, pumpingand conduit means for withdrawing the first stage product from the firststage collecting means and passing it to the second stage mixing means;conduit means for supplying water to the second stage mixing means, suchsecond stage mixing means being adapted to supply emulsion to theconduit means for supplying emulsion to the second stage distributormeans.

It is preferred that all three electrodes in the two stage desalter beenergized.

As adapted for serial stage desalting in three or more stages, theapparatus comprises a closed vessel provided with a plurality ofhorizontally disposed planar permeable electrodes in vertically spacedrelationship, the electrodes and the vessel interior being adapted andarranged to permit water to pass downwardly through the electrodes tothe lower portion of the vessel; first stage distributor means andconduit means for supplying oil-water emulsion thereto, such distributormeans being positioned at one side of the vessel and adapted to causethe emulsion to flow in a first stage treatment to the opposite side ofthe vessel between the bottom electrode and the electrode above it;means positioned at such opposite side of the vessel for collecting thetreated first stage product; second stage distributor means and conduitmeans for supplying second stage emulsion to the second stagedistributor means, the latter being positioned at the same side of thevessel as the first stage distributor means and adapted to cause thesecond stage emulsion to flow to the opposite side of the vessel betweenthe electrode next above the bottom one and the electrode next abovethat; means positioned at such opposite side for collecting the treatedsecond stage product; at least one additional stage distributor meansand conduit means for supplying additional stage emulsion to it, theadditional stage distributor means being positioned at the same side ofthe vessel as the other distributor means and adapted to cause theadditional stage emulsion to flow to the opposite side of the vesselbetween electrodes defining the respective remaining stages; meanspositioned at such opposite side for collecting the treated additionalstage products, except for the last stage; product withdrawal and outletmeans in the upper portion of the vessel; and water withdrawal means inthe lower portion of the vessel.

The above desalting apparatus is further provided with mixing means foreach stage and conduit means for supplying oil feed and water to eachmixing means, the mixing means being adapted to supply oil-wateremulsion to the corresponding distributor means; pumping means andconduit means for withdrawing products from the collecting means of eachstage other than the last and passing it to the mixing means for thesucceeding stage; and water supply means for each mixing means.

In an embodiment for parallel stage desalting and/or dehydratingemulsions the apparatus comprises a closed vessel provided with aplurality of coalescing stages, the stages being hydraulicallysubstantially independent; a plurality of horizontally disposed planarelectrodes in vertically spaced relationship defining these stages;distributor means for each stage at one side of the vessel andpositioned and adapted to cause emulsion to flow between adjacentelectrodes; common conduit means for supplying emulsion to eachdistributor means; product withdrawal and outlet means in the upperportion of the vessel; and water withdrawal means in the lower portion.The permeable electrodes and the vessel interior are adapted andarranged to permit water to pass downwardly through the electrodes tothe lower portion of the vessel.

In a preferred embodiment of the parallel stage treater, there are threeelectrodes defining two parallel stages and it is further preferred thatall of the electrodes be energized.

The apparatus includes mixing means adapted to supply emulsion to theconduit means for supplying emulsion to the distributor means; andconduit means for supplying feed and water to the mixing means.

The desalting/dehydrating apparatus is preferably provided with meansfor controlling the level of water in the lower portion of thetreating-vessel at a predetermined position.

The vessel is preferably horizontally elongated, being most preferablyin the form of a horizontal cylinder substantially longer in horizontallength than width. However, the vessel may be in the form of a sphere orof other suitable form.

The distributor means for each stage may be provided by a separatestructure or they may be incorporated in a single integral structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings:

FIG. 1 is a schematic transverse cross-section of one embodiment of thetreating apparatus of the present invention intended for serial stageoperation.

FIG. 2 is a longitudinal vertical cross-section taken along the line2--2 of the treater shown in FIG. 1; 2A and 2B being partial lengthsections taken in the direction of arrows 2A and 2B, respectively.

FIG. 3 is a schematic transverse vertical cross-section of anotherembodiment of the treating apparatus of this invention intended forserial stage operation.

FIG. 4 is a longitudinal vertical cross-section taken along line 4--4 ofthe treater shown in FIG. 3, 4A and 4B being partial length sectionstaken in the direction of arrows 4A and 4B, respectively.

FIG. 5 is a schematic transverse cross-section of a further embodimentof the treating apparatus of this invention intended for serial stageoperation.

FIG. 6 is a longitudinal vertical cross-section taken along lines 6--6of the treater shown in FIG. 5; 6A and 6B being partial length sectionstaken in the direction of arrows 6A and 6B, respectively.

FIG. 7 is a schematic transverse cross-section of an embodiment of thetreating apparatus of the present invention as adapted for three stageserial operation.

FIG. 8 is a schematic transverse vertical cross-section of an embodimentof the treater of the present invention as adapted for parallel stageoperation.

FIGS. 8a, 8b, 8c, 8d, 8e, 8f, and 8g illustrate modifications of thedistributor arrangement of FIG. 8.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIGS. 1 and 2 illustrate a two-stage serial desalter constituting oneembodiment of the invention. The desalter consists of a horizontallydisposed generally cylindrical vessel 1 having rounded ends 2, which maysuitably have a diameter of about 8 to 14 feet. Lengths of about 25 and49 feet and as much as 133 feet are suitable with a 12 foot diametervessel. Inside the vessel 1 are three horizontally disposed planarelectrodes 3, 4, and 5, which extend horizontally almost the entirelength and width of the vessel, but are not in contact with the sidesthereof. The electrodes 3, 4, and 5 are permeable, e.g., they may beformed of a grid of metal rods or pipes, suitably of cold finishedsteel, of a structure similar to that shown in U.S. Pat. No. 2,880,158to Delber W. Turner.

A distributor 6, serving as the first stage distributor, is positionedat one side of vessel 1 and extends longitudinally for most of thelength of the vessel. The distributor 6, shown here as a pipe with a rowof orifices 7 along its length, is positioned so that the orifices facethe interior of the vessel 1 at about midway between electrodes 4 and 5.Distributor 6 is supplied by mixing valve 8 via conduit 9. Mixing valve8 is supplied by raw oil conduit 10 and recycle water conduit 11, which,as shown, is connected with pump 12 and conduit 13 and/or a fresh watersource, not shown. An interstage outlet collector 14, which may be apipe with holes drilled therein, extends longitudinally along the sideof vessel 1 opposite the side at which distributor 6 is positioned, andis connected to conduit 15 which leads to oil recycle pump 16 and thenceto conduit 17. Conduit 18, connected to a fresh water source, leads intoconduit 17, which leads to mixing valve 19. A conduit 20 extends frommixing valve 19 to second stage distributor 21, shown here as similar tofirst stage distributor 6 and positioned at the same side of vessel 1,with a row of orifices 46 all along its length facing the interior ofthe vessel 1 at about midway between electrodes 3 and 4. An outletcollector 22, which may be a pipe with holes drilled in its upper wall,extends longitudinally along the top of vessel 1 and leads to outlet 23and treated oil effluent conduit 24. A water effluent conduit branchesoff from conduit 13.

Instead of the pipe distributors 6 and 21 shown, box type conduits asshown in the Martin patents above referred to, suitably modified to havethe orifices only on their inwardly facing sides, may be employed. Theconduits for the several stages may, if desired, be welded together.

The distributors 6 and 21 and collectors 14 and 22 may be supported fromthe vessel walls with angle clips, not shown, or by other conventionalmeans of support, e.g., hangers, guy wires, brackets, rails, etc.

As shown, electrodes 3, 4, and 5 are suspended by one or more insulators26, 27, and 28, respectively, and rods 29, 30, and 31, respectively,attached to the upper wall of vessel 1, as required to support theweight of the electrodes. As further shown, electrodes 3, 4, and 5 areeach energized individually by means of transformers 32, 33, and 34,respectively, the secondaries of which have one end grounded and connectvia conductors 35, 36, and 37, respectively, through entrance bushings38, 39, and 40, with the respective electrodes. However, it is alsocontemplated and within the scope of this invention that electrodes 3and 5 be energized and electrode 4 maintained at ground potential, inwhich case electrode 4 could rest on suitable rail bars, not shown,attached to the sides of vessel 1.

A potential difference of about 15,000 to 33,000 volts may suitably bemaintained between electrodes 3 and 4 and between electrodes 4 and 5. Athree phase current system may be employed to energize electrodes 3, 4,and 5. If electrode 4 is grounded, single phase current may be used toenergize electrodes 3 and 5, which are then opposed electrodes, or twolegs of a three phase current (3 phase open Δ) may be employed toenergize these electrodes.

In operation, the temperature of the raw oil is brought to the desiredtemperature by any suitable procedure, such as by heat exhange withanother refinery stream. The desired temperature will depend on thespecific gravity and type of feed. However, in many cases of crude oil,temperatures between 100° and 350° F., with about 250° F. being optimum,are used. The pressure must be sufficient to keep the oil and watermixture liquid at the operating temperature. A small amount, forexample, 1 pint per 1,000 barrels of oil, of a liquid demulsifier, e.g.,a Tretolite® DS series demulsifier, is optionally added to the oilprocessed.

As shown, crude oil is charged by conduit 10 and water is added viaconduit 11, which is supplied by recycle conduit 13. The amount of wateradded is suitably about 10% of the crude oil charged. The two fluids aremixed in mixing valve 8 to form an emulsion. The emulsion is carried byconduit 9 to the first stage distributor 6, from whence it flows betweenmiddle electrode 4 and bottom electrode 5 in a generally horizontaltransverse direction toward the opposite side of vessel 1, whereinterstage collector 14 is located. Water which has been thrown out ofemulsion by the electric field between electrodes 4 and 5 falls towardthe bottom of vessel 1, where a pool of collected water is maintained.The main portion of the treated oil is taken up by collector 14 and ispumped by interstage pump 16 through conduit 15 to conduit 17. A 5%addition of fresh water takes place in this conduit and is emulsifiedinto the oil by mixing valve 19. The second stge emulsion thus formed iscarried by conduit 20 to second stage distributor 21, from whence itflows between electrodes 3 and 4, substantially transversely in agenerally horizontal direction, to the opposite side of vessel 1. Thetreated oil passes upwardly near the edge of electrode 3 and along theside of vessel 1 and leaves the vessel by way of outlet collector 22,outlet 23 and conduit 24. The arrows shown in the FIGS. 1 and 2 indicatethe path of the fluids through the conduits and, in a general way,inside vessel 1.

The level of the interface 41 of the water with the treated oil may bemaintained automatically at the desired position in the lower portion ofvessel 1. As shown in FIGS. 1 and 2, this is accomplished by means ofmotor valve 42 on effluent conduit 25, which valve is actuated by afloat 43 connected to a control unit 44, which delivers an actuatingsignal through an interconnection, indicated by dashed line 45, to valve42. The float 43 senses the water level interface 41, and the valve 42is controlled to maintain the interface at the desired level in thelower portion of vessel 1. Various types of float and valve combinationsmay be employed as may be other types of level control means, such as anelectrical capacitance probe.

The exit velocity of the emulsion from the orifices 7 of the distributor6 should be such that there is enough initial energy to carry theemulsion in a substantially horizontal plane between the treatingelectrodes 4 and 5 to the interstage collector 14. The latter alsocollects some "override" of fluid from the second stage of treatment.The interstage pumping rate is controlled so that it exceeds the rate atwhich the treated oil is withdrawn from the treater by the second stageoutlet collector 22. This may be accomplished by operating the recyclepump 16 at a pumping rate 10 to 20% faster than the charging rate.

FIGS. 3 and 4 illustrate a desalter constituting another embodiment ofthe invention. This desalter is similar to that shown in FIGS. 1 and 2,the reference numerals corresponding to those employed in the latterfigures for the same features, except that a plurality of conduits 51and 52, which communicate hydraulically with each of the pipedistributors, shown here as 6a and 21a, respectively, extend downwardlyin arcs generally concentric with the side of the treating vessel 1.Conduits 51 and 52 are open at their bottom ends and are adapted to havetheir lower portions immersed in the water layer maintained in the lowerpart of the treating vessel 1. An interface 53 exists in the conduits 51and 52 between the water and the incoming emulsion, this interface beingat a lower level than the interface 41 between the water and oil layersin vessel 1. The pressure of the water acting upwardly on the emulsionsat interface 41, due to the differential head of water, forces theemulsions out of the orifices 7 and 46 in distributors 6a 21a,respectively, and into the treating spaces between electrodes 4 and 5and 3 and 4, respectively, with sufficient exit velocity to cause theemulsions to move in the paths described above in connection with FIGS.1 and 2. A distributor of this type is described and claimed inconcurrently filed application of Frederick D. Watson, Ser. No. 187,279,filed Sept. 15, 1980, which is hereby incorporated by reference. Withdistributors of this type, both will operate under the same differentialhead of water, but the flow rate through distributor 21a is made 10 to20% greater than that through distributor 6a by using larger orificeopenings, as shown, and/or by using a larger number of orifices. Threeconduits 51 and three conduits 52 per distributors 6a and 21a,respectively, may suitably be employed, although in very long treatersmore may be used. The operation of the desalter is otherwise asdescribed in connection with FIGS. 1 and 2.

Instead of the distributor means shown in FIGS. 3 and 4, a chambergenerally concentric with the wall of vessel 1 and having leg portions,open at their bottom ends, adapted to extend into the water layer may beemployed. A distributor of this type is also shown in the concurrentlyfiled Watson application PR 80-2A, above referred to and incorporated byreference.

Moreover, any of the "pan type" distributors of the prior art, e.g., asshown in Watson et al. U.S. Pat. No. 3,458,429, Mayse et al. U.S. Pat.No. 3,672,127, and Cole et al. U.S. Pat. No. 3,649,576, suitablymodified by being placed at a wall of vessel 1 and having the orificesonly on its inwardly facing side, may also be substituted for thedistributor means of FIGS. 3 and 4.

An embodiment of this invention employing a modified "pan type"distributor is shown in FIGS. 5 and 6. These figures illustrate adesalter also similar to that shown in FIGS. 1 and 2, the referencenumerals corresponding to those employed in the latter figures for thesame features, except that instead of pipe distributors 6 and 21,concentric, relatively narrow inverted troughs (or "pans") 6b and 21bare employed. Trough 21b is positioned immediately adjacent to andconcentric with a sidewall of vessel 1. Trough 6b is placed immediatelyadjacent to and concentric with trough 21b, the top 55 of trough 6bbeing at a lower level than the top 56 of trough 21b. The troughs arepositioned so that their open bottom ends will extend into the waterlayer maintained in the lower part of vessel 1. An interface 53b existsin both troughs between the water and the incoming emulsion, thisinterface being at a lower level than the interface 41 between the waterand oil layers in vessel 1. Troughs 21b and 6b are each provided with ahorizontal, inwardly facing row of orifices 7b and 46b, respectively.The orifices 46b in trough 21b are positioned in that portion of trough21b which extends above the top of trough 6b and face the space betweenelectrodes 3 and 4. The orifices 7b in trough 6b face the space betweenelectrodes 4 and 5. In a preferred form, as shown in FIGS. 5 and 6,troughs 6b and 21b are made integral with each other by sharing a commonwall 57 where they adjoin each other. Trough 6b is fed by conduit 9 andtrough 21b by conduit 20. The pressure of the water acting upwardly onthe emulsions at interface 41, due to the differential head of waterbetween that interface and interface 53b, forces the emulsions out ofthe orifices 7b and 46 b and into the treating spaces between electrodes4 and 5 and 3 and 4, respectively, with sufficient velocity to cause theemulsions to move in the paths described in connection with FIGS. 1 and2. The operation of the desalter is otherwise as described in connectionwith these figures.

The treaters described above may be adapted to three or more stagetreatment. FIG. 7 is a schematic representation of a verticalcross-section of a desalter employing three desalting stages in series.The reference numerals correspond to those employed in FIGS. 1 and 2 forthe same or similar features. In this embodiment, a fourth planar,horizontally disposed electrode 60 is employed in addition to the threeelectrodes 3a, 4a, and 5a, similar to those shown in FIGS. 1 and 2.Electrode 60 is positioned below electrode 5a. All the electrodes arepreferably energized, although, optionally, electrode 5a or 4a may be atground potential. An additional distributor 61, positioned betweenelectrodes 5a and 60, is employed in addition to distributors 6c and21c, and an additional interstage collector 62 is employed in additionto interstage collector 14a. The distributors are all shown as pipedistributors. In this embodiment, distributor 61 serves as the firststage distributor, distributor 6c as the second stage distributor, anddistributor 21c as the third stage distributor. Water for desalting issupplied to each desalting stage, fresh water being preferably employedin the third stage and recycle water in the first stage. The treatedproduct leaves the vessel 1 through outlet collector 22a and conduit 23aand water is removal through conduit 13. The various conduits, valvesand pumps removing and supplying fluids to and from the various stagesand the electrical circuitry are not shown, but their nature will beevident from the descriptions of the embodiments shown in FIGS. 1 and 2.

In an analogous manner to that of FIG. 7, desalters with more than threeserial stages may be constructed.

Any of the above described embodiments may be modified for operation ofthe stages in parallel rather than in series. As explained in the Martinpatents above referred to, parallel stage desalters have the potentialof doubling the oil handling capacity of a typical single stage system.

FIG. 8 is a vertical cross-section of a desalter having two parallelstages. The reference numerals in this figure correspond to thoseemployed in FIGS. 1 and 2 for the same or similar features. Raw oil isintroduced through conduit 10 and water through conduit 11a. The streamsare mixed in mixing valve 8 and introduced via conduit 9a intodistributor 65 having two distributor headers in the form of pipes 66and 67 adjacent to the sidewall of vessel 1, each pipe being providedwith a horizontal row of orifices, facing, respectively, the spacesbetween electrodes 4 and 5 and electrodes 3 and 4. The oil-water mixturethen flows in parallel paths between electrodes 4 and 5 and electrodes 3and 4 to the opposite side of vessel 1 and thence in a generally upwarddirection toward outlet collector 22 where the treated oil is withdrawn.The salt containing water is separated from the oil-water mixture by thepassage between the electrodes and drops downwards into the pool ofwater at the bottom of vessel 1. The level of this pool, represented byinterface 41a is maintained by effluent conduit 13 a, float 43, controlunit 44, interconnection 45 and motor valve 42, as described inconnection with FIGS. 1 and 2.

FIGS. 8a, 8b, 8c, 8d, 8e, 8f, and 8g illustrate modifications of thedistributor arrangement of FIG. 8. In FIG. 8a, the distributor headers66a and 67a are pipes as in FIG. 8, but are hydraulically connected toeach other inside vessel 1 by conduit 68, which is hydraulicallyconnected to feed conduit 9b. In FIG. 8b, a single box-like header 69,directly connected hydraulically to feed conduit 9b, is employed. Header69 is provided with two horizontal rows of orifices 70 and 71, whichface the spacing between electrodes 4 and 5, and 3 and 4, respectively.In FIG. 8c the distributor differs from that of FIG. 8 only in thatindividual box-like headers 72 and 73 are substituted for the pipeheaders 66 and 67 of FIG. 8. In FIG. 8d, the distributor similarlydiffers from that of FIG. 8a only in that individual box-like headers72a and 73a are substituted for the pipe headers of FIG. 8a. In FIG. 8e,a distributor similar to that of FIG. 8 is employed, except that theheaders 66b and 67b are provided with arcuate conduits 51a and 52a,respectively, open at their bottom ends and adapted to extend into thewater layer, as in FIGS. 3 and 4. In FIG. 8f, a distributor like that ofFIG. 8a is shown, except that header 66c is provided with arcuateconduits 74 similar to those shown in FIG. 8e. FIG. 8g shows adistributor like that of FIG. 8b, except that box-like header 69a isprovided with such a conduit 74a.

Distributor systems as shown in FIGS. 8e, 8f, and 8g are described andclaimed in the above referred to Watson application Ser. No. 187,279.

It is to be understood that all the electrode arrangements and potentialdifferences between electrodes disclosed for serial stage apparatus mayalso be employed for parallel stage apparatus and vice versa. Similarlypreferred process parameters such as oil temperature, oil pressure anddemulsifier addition, as described in connection with serial stageoperation apply also to parallel stage desalting.

As evident from the foregoing description, the nature of the distributormeans is not critical, so long as the distributor is positioned at oneside of the vessel and the emulsion is caused to flow to the oppositeside between adjacent electrodes in hydraulically substantiallyindependent flow. It will also be apparent that the invention is notlimited to a particular shape of vessel, electrical circuitry, voltageemployed, arrangement of conduits, interface level control means, etc.Many embodiments, modifications, developments and variations of formsare contemplated as long as they fall within the broad scope of theappended claims.

I claim:
 1. An apparatus for desalting oil-continuous oil-wateremulsions, said apparatus comprising a closed horizontally disposedvessel, generally cylindrical in form, which is provided therein withtwo hydraulically substantially independent coalescing stages, therebeing contained within said closed vessel: three horizontally disposedpermeable planar electrodes in vertically spaced relationship, each saidelectrode extending substantially the entire length and width of saidvessel; first stage distributor means and conduit means for supplyingoil-water emulsion to said first stage distributor means, said firststage distributor means extending longitudinally along one side of saidvessel; collector means extending longitudinally along the opposing sideof said vessel opposite said first stage distributor means; said firststage distributor means and said collector means being adapted to causesaid emulsion to flow in a first stage treatment transversely from saidone side to said opposing side of said vessel between the bottom andmiddle electrodes to form a first stage product; second stagedistributor means and conduit means for supplying a second stageoil-water emulsion to said second stage distributor means; said secondstage distributor means extending longitudinally along said one side ofsaid vessel and adapted to cause said emulsion to flow transversely in asecond stage treatment to the opposite side of said vessel between thetop and middle electrode; product collector means and outlet means inthe upper portion of said vessel; said permeable electrodes and thevessel interior being adapted and arranged to permit water to passdownwardly through said electrodes to the lower portion of said vessel;water withdrawal means in the lower portion of said vessel; first stagemixing means, conduit means for supplying oil feed and water to saidmixing means, said first stage mixing means being adapted to supplyoil-water emulsion to said conduit means for supplying oil-wateremulsion to said first stage distributor means; second stage mixingmeans, pumping and conduit means for withdrawing said first stageproduct from the first stage collector means and passing it to saidsecond stage mixing means; conduit means for supplying water to saidsecond stage mixing means, said second stage mixing means adapted tosupply second stage oil-water emulsion to said conduit means forsupplying said second stage emulsion to said second stage distributormeans.
 2. The desalting apparatus of claim 1, comprising also means forcontrolling the level of water in the lower portion of said vessel at apredetermined position.
 3. The apparatus of claim 1 wherein the top,middle and bottom electrodes are all energized.
 4. An apparatus fordesalting oil-continuous oil-water emulsions, said apparatus comprisinga closed horizontally disposed vessel, generally cylindrical in form,which is provided therein with a plurality of hydraulicallysubstantially independent coalescing stages, there being containedwithin said closed vessel: a plurality of horizontally disposed planarpermeable electrodes in vertically spaced relationship, the number ofsaid electrodes being one more than the number of stages, and each saidelectrode extending substantially the entire length and width of saidvessel; first stage distributor means and conduit means for supplyingoil-water emulsion to said frist stage distributor means, said firststage distributor means extending longitudinally along one side of saidvessel; first stage collector means extending longitudinally along theopposing side of said vessel opposite said first stage distributormeans; said first stage distributor means and said first stage collectormeans being adapted to cause said emulsion to flow in a first stagetreatment transversely from said one side to said opposing side of saidvessel between said bottom electrode and said electrode next above saidbottom electrode to form a first stage product; second stage distributormeans and conduit means for supplying a second stage oil-water emulsionto said second stage distributor means; said second stage distributormeans extending longitudinally along said one side of said vessel;second stage collector means extending longitudinally along saidopposing side of said vessel opposite said second stage distributormeans; said second stage distributor means and said second stagecollector means being adapted to cause said emulsion to flow in a secondstage treatment transversely from said one side to said opposing side ofsaid vessel between said electrode next above the bottom electrode andthe electrode next above said electrode next above the bottom electrodeto form a second stage product; at least one additional stagedistributor means and conduit means for supplying additional stageoil-water emulsion to said additional stage distributor means, saidadditional stage distributor means extending longitudinally along saidone side of said vessel; additional stage collector means extendinglongitudinally along said opposing side of said vessel opposite eachcorresponding stage distributor means, except for the last stage; saidadditional stage distributor means except for the last stage distributormeans and said additional stage collector means being adapted to causesaid additional stage emulsions to flow in additional stage treatmentstransversely from said one side to said opposing side of said vesselbetween the electrodes defining the respective additional stages;product collector means and outlet means in the upper portion of saidvessel, said permeable electrodes and the vessel interior being adaptedand arranged to permit water to pass downwardly through said electrodesto the lower portion of said vessel; water withdrawal means in the lowerportion of said vessel; mixing means for each stage and conduit meansfor supplying oil feed and water to each of said mixing means, saidmixing means being adapted to supply oil-water emulsion to said conduitmeans for supplying oil-water emulsion to each of said distributormeans; pumping means and conduit means for withdrawing products from thecollector means of each stage other than the last and passing it to themixing means for the succeeding stage; and means for supplying water toeach of said mixing means.
 5. The apparatus of claim 4 wherein there arethree stages.
 6. The apparatus of claim 4, comprising also means forcontrolling the level of the water in the lower portion of said vesselat a predetermined position.